The regulation of immunity by antibody and anti-receptor antibody is studied in mice immunized to phosphorylcholine. In the coming year we will attempt to answer two questions: Which cells are required for the production of anti-receptor antibody? Is specific anti-receptor antibody involved in the autogenous regulation of immunity to the antigen? To answer these questions we have recently developed: 1) a plaque assay method for demonstrating cells producing anti-receptor antibody and 2) a highly sensitive assay for serum anti-receptor antibody. To date we have demonstrated that 2 different T cell populations are required for the production of antibody to phosphorylcholine and anti-receptor antibody and that an individual mouse immunized with phosphorylcholine repeatedly produces antibody and specific anti-receptor antibody.